The concept of the in-situ purification island mentioned above means the facilities to naturally purify the polluted water system of rivers or lakes, constructed with the bed of river or lacustrine as the carrier.
As an important carrier of natural resources and the environment, rivers and lakes have the economic functions as flood controlling and drainage, farm irrigation, water supply, shipping and farming, and the ecological functions as providing habitat and thereby reflecting biodiversity, climate regulation, improvement of the environment, shaping the landscape and water conservation, which has an important realistic and future significance to the rise and fall of the city and the economic development and prosperity.
Although the protection of water environment has become the consensus of the people, a lot of industrial and urban sewage is discharged directly to rivers and lakes without required treatment due to the limitation of variety of subjective and objective conditions, which pollutes the water bodies and also damages the bed soil of rivers and lakes. Especially when the water is contaminated by such as nitrogen, phosphorus, organic pollutants and various heavy metals elements, the situation of water sub-quantity becomes more seriously. Therefore, the improvement of water treating ability and water treating efficiency to make use of sewage has a positive realistic and long-term significance for solving the scarceness of water resource in our country.
Due to the advantages such as no occupying the ground, no interference from the building on the ground, saving the investment, no energy consumption, tending to be maintenance-free and good and long effect of water-repairing, improving the water quantity based on the natural purification mechanism of water in the rivers is recognized in the field and gradually becomes a trend. However, because of large flow of river and complex morphology and the natural purification of water is a complex process affected by many factors, it will not only cost high in construction, operation and maintenance but also has poor landscape according to the conventional treatment of sewage.
The technical information about natural purification of river water can be found in the published Chinese patent documents, typically as the “a high-hydraulic loading soil percolation system” recommended by CN203247173U, which consisted of a surface covering layer, a water distributing groove, a water distributing tank arranged in the water distribution groove, a first artificial filler, a bottom supporting layer and a water outlet pipe. The point is that to arrange a clay pan between the first and the second artificial filling layers, and both the first and the second artificial filling layers are consisted of fine particles and coarse particles of vermiculite layers, in which the fine layer is above the coarse one. Although technical effect in the paragraph 0010 of description can be achieved, the solution in the patent still has disadvantages: firstly, it's construction tedious due to the need of laying pipelines (distributing pipe and outlet pipe), and it's difficult or impossible to repair once the pipe blocked; secondly, the risk of the outlet pipe blocking is high because the first and the second filling layers are consisted of fine and coarse particles separately and the outlet pipe is arranged in the bottom; thirdly, it's difficult if not impossible to intercept point source pollution in river because of the limitation of the construction. Another solution provided by CN103395930A is “an ecological slope protection type sewage land infiltration system and the infiltration method thereof”, in which a grid pond, an anaerobic hydrolyzing pond and a stepped land infiltration unit are arranged sequentially along the gradient of a sloping field from top to bottom to form a stepped (also known as terraced) structure, but it has the disadvantages such as the high construction cost, the difficulty in construction, the high operation consumption and the poor landscape, at the same time, it is often with special requirements to the slope of the river.
According to the prior art above, there is a need to improve, so the applicant made some useful exploration and finally formed the technical solution will be introduced following. And the results proved to be feasible after the repeated deduction experiments under the security measures.